Disclaimer: If you recognize it, I don't own it.
A sudden hush fell over the battlefield. Ace slowly opened his eyes, wondering where the pain was. A glance at Luffy showed his brother was staring wide-eyed at something behind him. Glancing over his shoulder Ace froze. Standing between the D brothers and Akainu was what looked like a small golden dragon with no wings, its face reminiscent of a horse with back-sweeping antlers lowered threatening towards the attacking admiral. A translucent shield stood between the two, blocking Akainu's magma fist.
All eyes were on the creature as it turned to the brothers, hoofed feet making no sound and leaving no tracks on the scorched ground as it walked past Ace and stopped before Luffy. "Is that…?"
"I think it is."
"A kirin." Pirates and marines alike murmured in wonder as the kirin locked gazes with Luffy, pure blue meeting startled brown. Ace tense when Luffy gasped, mouth falling open. Whatever the kirin was searching for it must have found. Slowly, the sacred beast lowered onto its front knees, head brush the ground as it bowed low. Ace forgot to breath, mind racing over the legends of kirin appearing before great kings.
An enraged scream broke the silence, causing Ace to nearly jump out of his skin, flames bursting to life on his arms and back as he searched for the threat, quickly spotting Blackbeard rushing towards the crowd with his eyes locked on Luffy. The kirin's ears flicked back as it rose to its feet, trotting between Luffy and Blackbeard and rearing back on its hind legs. A small ball of light appeared between the kirin's antlers briefly before launching at Blackbeard, knocking the angry pirate to the ground. A swirling cloud of smoke-like darkness rose from Blackbeard, a small humanoid figure visible within before the smoke dissipated.
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If asked later Ace would never be able to recount exactly how but everyone somehow made it safely back to the ships. At the moment Ace was nestled safely in his father's arms, surrounded by his sworn-brothers and -sisters. Luffy stood not far away stroking the kirin's silky mane. "You know, it'd be awesome if you were a real kirin." Luffy commented, drawing glances from the surrounding crew.
"Whata ya mean, Lu?" Ace asked, sitting up slightly to get a better look. He didn't see anything that might suggest the kirin wasn't the real deal. In answer, however, the kirin threw its head back and let out a loud laugh.
"Saw right through me from the start, didn't ya? Good ta see you developin' a bit o' sense." It - he? - said, still chuckling. "So what gave me away?"
"Silly, I'd know my big brother anywhere." Luffy announced, throwing his arms around the kirin's neck with a laugh. The 'kirin,' who was apparently a Mythical Zoan like Marco, laughed again as he shifted back to his human form, one arm snaking around Luffy's waist while the other dug into the blue shoulder bag he was wearing and pulled out a familiar top hat.
"Sa…?" Ace trailed off, eyes wide and staring at the dead-man come back from the grave.
"Hey, Ace. Didja miss me?" Sabo asked, returning his hat to its proper place on his head and grinning. Yes, fainting sounded very good right then, so Ace did.
END
A few notes on Sabo's Devil Fruit. Appearance-wise, I see him with a horse- or deer-like body with slim legs and split hooves like a deer, but covered in golden scales and with a reptilian tail, which to Ace made him look like a wingless dragon. The antlers mentioned are similar to a Chinese dragon and the ears are horse-like. As to his powers he can 'cleanse' other Devil Fruit users of their power, a technique he calls his Cleansing Light which is what he used on Blackbeard. He can also block attacks base on Devil Fruit powers with his Purifying Shield, but only purely Devil Fruit based attacks. One of Luffy's punches would go right through it because its still a physical attack, his scales do offer a considerable defense in this area, however. To offset this and keep him from being too-powerful his fruit comes with an additional weakness, he can't harm others. If he tries to attack someone, either directly or indirectly, his body falls limp and he feels like he was just dropped into the ocean. His Cleansing Light does not count as an attack because he is 'freeing' his target from their 'burden.'
Also, the humanoid figure in the smoke was the Sea Devil from the Yami-Yami no mi. The Yami-Yami no mi was not destroyed, simply purged from Blackbeard's body. It will regrow/reappear in another part of the world after a few days.
Edit: Tweaked a few things, mostly fixing typos and spots that did sound right. Also extended the description of Sabo's Devil Fruit.